The objective of this study is to investigate the impact of sugar sweetened beverages on the fat metabolism of healthy young men. It is well known that consumption of beverages sweetened with fructose is associated with different health risks such as type 2 diabetes. The present study has been designed to dissect differences in the metabolic pathways of fructose and glucose, but also metabolic adaptations during fructose, glucose and sucrose diets. During a period of seven weeks subjects will consume either fructose, glucose or sucrose sweetened beverages or continue their usual drinking habits. During these seven weeks there will be different metabolic investigations using stable isotope tracers. First, the rate of lipolysis and beta-oxidation will be determined. Second, the rates of fatty acid synthesis will be measured. During all examinations there will also be substrate- and energy-utilization measurements by indirect calorimetry, blood analysis and morphometric measurements. Based on the literature main hypotheses are: Fructose enhances de novo lipogenesis postprandially and also in the fasting state significantly more than glucose by enhanced expression of lipogenic enzymes. Fructose decreases beta oxidation via downregulation of oxidative enzymes.